System for adjusting color intensity of neighboring pixels

ABSTRACT

A system for printing an image onto a substrate includes a print controller that determines a difference in intended color intensity between a first pixel and a second pixel; adjusts the intended color intensity of the first pixel based on the determined difference; and deposits a colorant onto the substrate at the first pixel at the adjusted intended intensity, so as to enhance the appearance of the image on the substrate. The current system has particular utility in enhancing the appearance of fine images such as one pixel wide, vertical and diagonal lines in a printing system which utilizes printhead heating elements that are larger in the vertical direction than in the horizontal direction.

This is a continuation of application Ser. No. 07/919,864 filed Jul. 27,1992 now abandoned.

1. Field of the Invention

This invention relates to a system and method for enhancing the visualappearance of a fine image, such as a thin line, during printing. Morespecifically, the invention relates to improving the appearance of suchan image in an intensity-variable type printing system utilizing pixelswhich are larger along a first axis than along a second axis.

2. Description of the Prior Art

Intensity-variable printing is, for the purposes of this document,defined as any type of printing in which colorant may be deposited on abase unit area, or pixel, in more than one intensity or degree ofdilution. Diffusion printing, which is defined as including both commondye-diffusion and sublimation dye printing techniques, is one type ofintensity-variable printing. Other intensity-variable printingtechniques may include continuous ink jet printing, variable spot-sizedphase change ink jet printing, variable dot electrophotography, variabledot thermal transfer printing, laser-induced dye diffusion transferprocesses, dry silver technology and photographic printing, as well asothers.

Dye diffusion printing involves the transfer of a dye colorant from acarrier, such as a polymer ribbon, onto a specialized substrate surface,such as a polyester sheet or a coated sheet of ordinary paper, in acontrolled manner to generate an image. A thermal transfer print enginehaving an array of electrically actuatable heating elements is typicallypositioned so that the ribbon is juxtaposed between the printheadelements and the substrate. The amount or intensity of dye deposited ata single location or pixel on the substrate can be varied by adjustingthe electrical input to the printhead elements. When one or more of theprinthead elements is heated, the dye/carrier structure is heated to atemperature sufficient to cause migration of a commensurate amount ofdye to the substrate. By using a ribbon or ribbons having the threeprimary or subtractive colors, or those colors plus black, highly subtlecolorant gradations may be achieved on the substrate. Images of nearphoto quality have been produced using dye diffusion technology.

One characteristic of print heads that are used in sublimation dyeprinting, diffusion dye printing or the like is that the height of eachprint head heating element is larger than its width. In other words,each print head heating element is rectangular, rather than square. Forexample, the pixel shape on Sharp Electronics Model JX561 print head isa rectangle having a height to width ratio of approximately 2 to 1.

This hardware characteristic creates some problems during printing. Forexample, as may be seen in FIG. 1, vertical single-pixel lines arenoticeably thinner than horizontal single-pixel lines. To compensate forthe height of the rectangular heating elements, a portion of the twovertically adjacent pixels is overlapped as shown in FIG. 1. The dottedline shows the bottom of the rectangular heating element. Theoverlapping corrects some of the distortion. For example, 3pixels-by-3-pixels square is achieved by the partial vertical overlapwithout further correction. A space between horizontal heating elementsdoes not cause any visible break in the printed horizontal line.Diffused dye from the adjacent heating elements diffuses and closes thegap on the substrate. However, this correction does not helpsingle-pixel lines. Diagonal single-pixel lines are also affected bysuch a print head and tend to appear jagged and inconsistent.Consequently, small point size text tends to lose definition due to therectangular-shaped printhead elements.

Furthermore, there are thermal issues that make it difficult for theprinter to securely deposit a single pixel which is isolated from thenext horizontal pixel. When only one printhead element is heated, rapiddissipation of heat from that element to adjacent structure on theprinthead and to the carrier ribbon sometimes causes insufficientheating of the ribbon to induce the intended amount of colorantdeposition. Since the print head elements are arranged as a horizontallinear array horizontally isolated pixels will not be protected againstsuch heat loss effects, even when the desired image requires avertically adjacent pixel to be printed upon.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a system andmethod which is adapted to compensate for the visual distortions of afine image, such as one pixel-wide lines, small size text and isolatedsingle pixels, which is printed by a printhead having rectangularheating elements.

It is an object of one aspect of the invention to provide an enhancedvisual appearance of the fine images so that they will appear as wide asthe longest edge of the rectangular heating elements.

It is another object of the invention to prevent poor printing qualitywhich might otherwise result from rapid dissipating of heat from theheating elements when horizontally isolated pixels are being printed.

It is yet another object of the invention to limit such enhancement, sothat the enhancement does not result in unwanted distortion of theimage.

To achieve the above and other objects of the invention, a method ofprinting an image onto a substrate may include the steps of determininga difference in intended color intensity between a first pixel and asecond pixel; adjusting the intended color intensity of the second pixelbased upon the difference in the above step; and depositing a colorantonto the substrate at the first pixel and at the second pixels at theadjusted intended intensity, thereby enhancing the appearance of theimage on the substrate.

A method of printing a minute image onto a substrate using a rectangularprint head element according to a second aspect of the invention mayinclude the steps of selecting a subset of contiguous pixels;determining if a difference in color intensity between a first of thecontiguous pixels and a second of the contiguous pixels is above apredetermined value; adjusting the color intensity of the second pixel;repeating the above steps until all pixels are examined; and depositinga colorant onto the substrate according to the adjusted colorintensities, whereby the deposited color according to the adjusted colorintensities will compensate for distortion caused by the rectangularprint head element and enhance an appearance of an image on thesubstrate.

A system of printing an image on to a substrate according to the thirdaspect of the invention may include a print controller which determinesa difference in color intensity between a first pixel and a secondpixel; which adjusts the color intensity of the second pixel based uponthe difference; and which sends control signals instructing the printhead to deposit a colorant on to the first and second pixels on thesubstrate according to the adjusted color intensity, thereby enhancingthe appearance of the image on the substrate.

A system of printing a minute image on to a substrate using arectangular print head element according to a fourth aspect of theinvention may include a print controller which selects a subset ofcontiguous pixels; which determines if a difference in color intensitybetween a first of the contiguous pixels and a second of the contiguouspixels is above a predetermined value; which adjusts the color intensityof the second pixel; and which sends control signals instructing theprint head to deposit a colorant on to the substrate according to thecolor intensity, whereby the deposited color according to the adjustedcolor intensity will compensate for a distortion caused by therectangular print head element and enhance the appearance of the imageon the substrate.

A method of operating a printing apparatus comprising a plurality ofheating elements adapted to be juxtaposed to a carrier comprising acolorant for printing on a substrate according to fifth aspect of theinvention may include the steps of determining a difference in colorintensity between a first pixel and a second pixel; adjusting the colorintensity of the second pixel based upon the difference in the abovefirst step; and energizing a set of heating elements corresponding tothe position of a colorant to be applied on to the substrate accordingto the color intensity, whereby the deposited color according to theadjusted color intensity will enhance the appearance of the image on thesubstrate.

An apparatus for printing an image on to a substrate according to afifth aspect of the invention may include a print controller whichdetermines a difference in color intensity between a first pixel and asecond pixel; which adjusts said color intensity of the second pixelbased upon the difference; and which sends control signals instructingthe print head to energize a set of heating elements corresponding tothe position of a colorant to be applied on to the substrate accordingto the adjusted color intensity, whereby the deposited color accordingto the adjusted color intensity will enhance an appearance of the imageon the substrate.

The invention also embraces printing systems and printed products whichcorrespond to the inventive methods.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a visual distortion of lines printed bya printhead with rectangular heating elements.

FIG. 2A is a diagram of a letter "E" printed by the same rectangularheating elements.

FIG. 2B is a diagram of a letter "E" printed by square heating elementsand has the same number of pixels as FIG. 2A.

FIG. 3 illustrates an enhancement of the vertical and diagonal linesshown in FIG. 1, according to a preferred embodiment of the invention.

FIG. 4 illustrates an enhancement on the letter "E" shown in FIG. 2Aaccording to a preferred embodiment of the invention.

FIG. 5A is a diagram of horizontally isolated pixels that are apart bymore than one pixel.

FIG. 5B illustrates an enhancement over the horizontally isolated pixelsas shown in FIG. 5A according to a preferred embodiment of theinvention.

FIG. 6 is a diagram of horizontally isolated pixels that are apart byonly one pixel, and this pattern of pixels is not enhanced by apreferred embodiment of the invention.

FIG. 7 shows a window which contains four pixels under examination foran enhancement according to one embodiment of the invention.

FIG. 8 is a flow chart depicting detailed processes of enhancing a fineimage according to a preferred embodiment of the invention.

FIG. 9A illustrates an existing three-pixel-wide vertical line whoseouter columns of the pixel have a lighter color intensity.

FIG. 9B shows an enhancement of the three-pixel wide vertical line shownin FIG. 9A by providing a more desirable contrast in color intensitybetween the surrounding and center columns of pixels.

FIG. 10 is a schematic depiction of a thermal mass transfer printingsystem according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views, and referring inparticular to FIG. 1, one horizontal line, one vertical line and onediagonal line are depicted as printed by the printhead that hasrectangular heating elements. Such heating elements are activated tomelt dye such as diffusion dye or sublimation dye to deposit the dye onthe surface of a substrate. For the purpose of this document, the pixelis an abstract concept which refers to the extent of an area where dyeis deposited by one heating element. Any image is constructed byprinting combinations of single pixels, and each pixel has an identicalrectangular shape with a substantially 2 to 1 ratio between the heightand the width. Because of this ratio, the single-pixel-wide verticalline in FIG. 1 appears thinner than a single-pixel-wide horizontal line.A single-pixel-wide diagonal line also appears inconsistent due to therectangular pixel. These visual distortions are not limited to theabove-described graphical primitives, but are also manifested in morecomplex graphics such as small size font. The legend on the side showsthat the original line has the color intensity value of 15, while thebackground has the color intensity value of zero.

Referring now to FIG. 2A, a letter "E" looks more unproportional than anormal counterpart, FIG. 2B. Although the letter "E" in FIG. 2A has thesame number of pixels as FIG. 2B, the letter "E" in FIG. 2A appears tohave thicker horizontal line segments than the vertical line segment.The letter "E" as shown in FIG. 2B, however, will lose its proportionwhen it is printed by a printhead with non-square heating elements. Itis an object of the invention to solve the above described problems inintensity-variable printing systems. The legend on the side shows thatthe original line has the color intensity value of 15, while thebackground has the color intensity value of zero.

By using intensity-variable printing technology, it is possible tocreate a different shade of color by varying the amount of deposited dyeon the substrate surface. Conceptually speaking, to make thesingle-pixel vertical line appear as wide as the single-pixel horizonalline, an additional lighter color single-pixel line is juxtapiosed nextto one or more, and preferably both, sides of the single-pixel verticalline.

Referring to FIG. 3, the lines shown in FIG. 1 are compensated by thejuxtaposed lines. The compensated vertical line in FIG. 3 is threepixels wide. An additional single-pixel-width line is juxtaposed on eachside of the original single-pixel vertical line to enhance the width.The color intensity of the juxtaposed line is approximately half that ofthe original single-pixel vertical line. The legend on the side showsthat the original line has the color intensity value of 15, while thebackground has the color intensity value of zero. The compensating linehas the color intensity value of 7.5. However, since the new verticalline is now three pixels wide, the distortion caused by the 1:2 ratiorectangular pixels seems overcompensated, as may be seen in FIG. 3.However, the enhanced vertical line in the actual print appears as wideas a single-pixel-wide horizontal line, and each row in the enhancedvertical line now appears substantially square rather than rectangular,because of the lighter shade of the compensating adjacent pixels.Accordingly, a human will perceive the enhanced vertical line as beingsomewhat narrower than it actually is.

Still referring to FIG. 3, the diagonal line is also compensated for,according to a preferred embodiment of the invention. One pixel on eachside of the pixels in the original single-pixel-wide diagonal line isadded to enhance the width the; appearance of the line. These juxtaposedpixels have approximately half the intensity of the original diagonalline. As for the vertical line, the enhanced diagonal line in the actualprint appears as wide as a single-pixel-wide horizontal line, and eachrow now appears substantially square rather than rectangular.

Referring now to FIG. 4, the same enhancement is applied to the letter"E," as depicted in FIG. 2A. Some pixels have been added along someportions of the vertical line in FIG. 4. The intensity of theseadditional pixels is approximately half of that of the original pixels.The legend on the side shows that the original line has the colorintensity value of 15, while the background has the color intensityvalue of zero. The compensating line has the color intensity value of7.5. Although the enhanced character has not changed its overall height,it has gained a better proportion between the vertical and horizontallines. As a result, the enhanced character appears aesthetically moreacceptable. Such effect is more readily appreciated in some charactersor numbers that have a sharp contrast between the vertical andhorizontal line components. On the other hand, other characters such as"0" (underscore) and "-" (hyphen) are not affected by the preferredembodiment of the invention.

Referring now to FIGS. 5A and 5B, similarly horizontally isolated singlepixels as shown in FIG. 5A are enhanced by the above-described preferredembodiment of the invention. FIG. 5B shows the enhanced horizontallyisolated single pixels. The legend on the side shows that the originalpixels have the color intensity value of 15, while the background hasthe color intensity value of zero. The compensating pixels have thecolor intensity value of 7.5. These horizontally isolated single pixelsare not visually distorted as much as the vertical single-pixel line.Because there is no comparison such as the case between the vertical andhorizontal line, there is less need for correcting the appearance of thehorizontally isolated single pixels. However, as discussed above, it isdifficult for some printers to accurately deposit dye over ahorizontally isolated single pixel area on the substrate due to heatdissipation from the single activated heat element. Thus, because of thethermal issue of the print head, the enhancement of the horizontallysingle pixel is also preferred.

On the other hand, a certain pattern such as shown in FIG. 6 should notbe altered by the preferred embodiment of the invention so as not todestroy the original pattern. Accordingly, it is important that theenhancement should be somewhat limited so that it is applied only to thesingle-pixel-wide vertical and diagonal lines as well as certainhorizontally isolated single pixels. For example, since these lines orpatterns can be a part of some alpha-numeric characters or othersymbols, an overenhancement may make these characters and symbolsunrecognizable. Thus, the preferred embodiment of the invention enhanceshorizontally isolated single pixels only if they are separated by morethan one pixel apart.

To accomplish the above described enhancement, according to onepreferred embodiment of the invention, four horizontally contiguouspixels are examined at a time as shown in FIG. 7. Prior to printing, thevalues of the four pixels corresponding to the upper left corner of asubstrate are loaded into a one-dimensional array called Window, whichis designated by w[0] through w[3]. When these pixel values are examinedand processed, Window is shifted by one pixel as shown by the dottedline in FIG. 7. When all the pixels in the same row are processed,Window is moved down to the next row and the process continues. This isrepeated until all the pixels on the raster data array are considered.

Referring now to FIG. 8, a flow chart of a software process forimplementing the enhancement technique of the invention is furtherdescribed in detail. After the four-bit (which in binary numbering canrepresent values of 0-15) data of the intensity level for each of thefour horizontally contiguous pixels is loaded from the raster data arrayinto Window, three conditions are tested. These tests include: 1)whether a difference in the pixel intensity value between the second andfirst pixels (w[1]-w[0]) is more than 8, 2) whether a difference in thepixel intensity value between the second and third pixels (w[1]-w[2]) ismore than 8, and 3) whether a difference in the pixel intensity valuebetween the second and fourth pixels (w[1]-w[3]) is more than 8. Whenall of the three conditions are satisfied, the first pixel intensityvalue is adjusted to an average of the first and second pixel intensityvalues as shown in w[0]:=(w[0]+w[1])/2. Similarly, the third pixelintensity value is adjusted to an average of the second and third pixelintensity values as shown in w[2]:=(w[2]+w[1])/2. On the other hand, ifany of the three conditions is not met, no pixel intensity value isadjusted. Then the content of the Window array, w, is stored back intothe raster data array, and the Window frame is moved to the right by onepixel or the beginning of the next row upon finishing the last fourpixels on the row. Until all the pixel values in the raster data arrayare examined, the above described process is repeated.

Still referring to FIG. 8, the preferred embodiment may affect any pixelwhich is adjacent to a pixel having a pixel intensity value of 9 orgreater, provided that the above described conditions are met.Accordingly, a single-pixel-wide vertical line with its pixel intensityvalue over 8 with a zero intensity background is enhanced to have 50%intensity pixels on both sides of the original line.

According to the preferred embodiment, the above-described enhancementis not limited to single-pixel-wide lines. For example, a vertical3-pixel-wide line as shown in FIG. 9A may be also enhanced to one shownin FIG. 9B. FIG. 9A diagrammatically shows a 3-pixel-wide vertical linehaving the center pixel intensity of 15 and the adjacent pixel intensityof 1 with the background of zero intensity. Since the difference in thepixel intensity is more than 8 between these columns of pixels and thesecond column right to the center column of pixels has 0 intensity, allthe three conditions described in reference to FIG. 8 are satisfied.Thus, the adjacent columns of the pixels will have the intensity levelof 8 as shown in FIG. 9B after the enhancement. The enhancement of thiskind is not necessarily spatial as discussed in reference to FIGS. 1-6,but intensity-related. Because of more desirable contrast of 50%intensity in FIG. 9B, the vertical line substantially improves itsappearance so that its width is more likely perceived as that of thehorizontal line. A similar type of enhancement can be applied to asituation where the difference in color intensity between a single-pixelline and the non-zero color intensity background is more than eight.

FIG. 10 depicts an intensity-variable printing system 10 according to apreferred embodiment of the invention, which is preferably adiffusion-type printing system. System 10, designed to print an image ona substrate 12, includes a printhead element 16, which is responsive tocommands from a printer controller 18. Printhead 16, according to thepreferred embodiment of the invention, includes a linear array ofheating elements 20, each of which may be heated in response to acommand from the printer controller 18 by electrical resistance. Eachheating element is intended to be aligned with discrete unit areas orpixels on the substrate 12. As will be appreciated by those skilled inthe art, printer controller 18 includes a processor for selectivelycontrolling print head 16 and heating elements 20 during the printingprocess. In accordance with the invention, the processor of printercontroller 18 is controlled by software which implements the flow chartof FIG. 8 for providing intensity-variable printing.

A printer ribbon 24 is interposed between heating elements 20 and thesubstrate 12. Printer ribbon 24 includes a carrier layer, and a colorantlayer containing a dye or colorant that is designed to migrate to thesubstrate upon application of heat from one or more of the heatingelements 20. For dye-diffusion printing, the ribbon 24 contacts thesubstrate 12, and the colorant migrates into the substrate on amolecular level. For sublimation dye printing, there is no contactbetween the ribbon and the paper, and heat from the heating elementscauses the colorant to sublimate, or phase from solid to gas, adjacentto the substrate, causing absorption in to the substrate 12. The surfaceof substrate 12 must be chemically compatible with the dye of colorantfor printing to be successful, as is well known to those having ordinaryskill in this technology.

System 10 is preferably a color printing system, and ribbon 24preferably includes different portions, each having colorant impregnatedthereon, which correspond to the three primary or subtractive colors.Optionally, a black portion may also be included. More than one ribbon24 may also be used to accomplish transfer of the different colorants tothe substrate, if desired.

A support roller 22 or equivalent surface is provided to supportsubstrate 12 in parallel spaced relationship with respect to heatingelements 20. By selectively controlling the heating elements 20 onprinthead 16, printer controller 18 is constructed to control theplacement of an image onto the substrate 12, as was described above inreference to FIGS. 7 and 8.

Preferably, printhead 16 is obtainable from Sharp ElectronicsCorporation as Model No. JX561. Preferably, ribbon 24 is the printerribbon which is obtainable from Sharp Electronics under Model No.A4JX61R3T, which is a three color ribbon having a cyan component, amagenta component, and a yellow component. Alternative ribbon models mayinclude Sharp Electronics Model No. A4JX61R4T, which is a four colorribbon having a cyan component, a magenta component, a yellow component,and a black component. A black ribbon, which may be used alone or inconjunction with the three or four color ribbons, is obtainable fromSharp Electronics under Model No. A4JX61RBT.

It is understood, however, that even though numerous characteristics andadvantages of the present invention have been set forth in the foregoingdescription, together with details of the structure and function of theinvention, the disclosure is illustrative only, and changes may be madein detail, especially in matters of shape, size and arrangement of partswithin the principles of the invention to the full extent indicated bythe broad general meaning of the terms in which the appended claims areexpressed.

What is claimed is:
 1. A system for printing an image comprising aplurality of pixels onto a substrate, comprising:a print head whichselectively deposits a colorant onto said substrate in response to printcommands; and a programmable print controller which determines a firstdifference in color intensity between a second pixel and a first pixelin said image, determines a second difference in color intensity betweenthe second pixel and a third pixel in said image, determines a thirddifference in color intensity between the second pixel and a fourthpixel in said image, adjusts the color intensity of the first pixel andthe color intensity of the third pixel if said first, second and thirddifferences in color intensity each exceeds a predetermined thresholdvalue, and sends a print command to said print head instructing saidprint head to deposit the colorant onto said first pixel on thesubstrate according to said adjusted color intensity of said first pixeland to deposit the colorant onto said third pixel on the substrateaccording to said adjusted color intensity of said third pixel so as toenhance the appearance of the image on the substrate.
 2. A system asrecited in claim 1, wherein said first pixel and said second pixel areadjacent.
 3. A system as recited in claim 1, wherein said programmableprint controller adjusts said pixel color intensity of said first pixelto an average intensity of said first pixel and said second pixel.
 4. Asystem as recited in claim 1, wherein said first pixel and said secondpixel are near an edge of the image.
 5. A system as recited in claim 1,wherein each of said pixels is monochromatic.
 6. A system as recited inclaim 1, wherein each of said pixels further comprises a plurality ofcolors.
 7. A system as recited in claim 1, wherein said programmableprint controller adjusts said color intensity of said third pixel to anaverage intensity of said second pixel and said third pixel.
 8. A systemfor printing an image comprising a plurality of pixels onto a substrate,comprising:a printer having a rectangular print head which selectivelydeposits a colorant onto said substrate in response to print commands;and a programmable print controller which selects a subset of saidplurality of pixels defining adjacent pixels, determines a firstdifference in color intensity between a second pixel of said adjacentpixels and a first pixel of said adjacent pixels in said image,determines a second difference in color intensity between the secondpixel and a third pixel of said adjacent pixels in said image,determines a third difference in color intensity between the secondpixel and a fourth pixel of said adjacent pixels in said image, adjuststhe color intensity of the first pixel and the color intensity of thethird pixel if said first, second and third differences in colorintensity each exceed a predetermined threshold value, and sends a printcommand to said print head instructing said print head to deposit thecolorant onto said first pixel on the substrate according to saidadjusted color intensity of said first pixel and to deposit the colorantonto said third pixel on the substrate according to said adjusted colorintensity of said third pixel, whereby the colorant deposited accordingto said adjusted color intensities of said first and said third pixelscompensates for distortion caused by the rectangular print head andenhances the appearance of the image on the substrate.
 9. A system asrecited in claim 8, wherein said subset is a set of horizontallyadjacent pixels on the substrate.
 10. A system as recited in claim 8,wherein said pixels of said subset are adjacent in a direction in whicha shorter edge of the rectangular print head elements extends.
 11. Asystem as recited in claim 8, wherein said first and said second pixelsare immediately adjacent to each other.
 12. A system as recited in claim11, wherein said first and second pixels are at least two pixels awayfrom each other.
 13. A system recited in claim 8, wherein an intensityof said first pixel is adjusted to an average intensity of said firstand said second pixels.
 14. A system as recited in claim 8, wherein eachof said pixels further comprises a plurality of colors.
 15. A system asrecited in claim 8, wherein the color intensity of said third pixel isadjusted to an average intensity of said second pixel and said thirdpixel.
 16. A system for printing an image comprising a plurality ofpixels onto a substrate, comprising:a print head having heating elementswhich selectively deposit a colorant onto said substrate in response toprint commands; and a programmable print controller which determines afirst difference in color intensity between a second pixel and a firstpixel in said image, determines a second difference in color intensitybetween the second pixel and a third pixel in said image, determines athird difference in color intensity between the second pixel and afourth pixel in said image, adjusts the color intensity of the firstpixel and the color intensity of the third pixel if said first, secondand third differences in color intensity each exceeds a predeterminedthreshold value, and sends a print command to said print head whichenergizes a set of said heating elements corresponding to the positionof the colorant to be applied onto said first pixel on the substrateaccording to said adjusted color intensity of said first pixel and ontosaid third pixel on the substrate according to said adjusted colorintensity of said third pixel, whereby said colorant applied accordingto said adjusted color intensities of said first and said third pixelsenhances the appearance of the image on the substrate.
 17. A system asrecited in claim 16, wherein said first pixel and said second pixel areadjacent.
 18. A system as recited in claim 16, wherein said programmableprint controller adjusts said color intensity of said first pixel to anaverage intensity of said first pixel and said second pixel.
 19. Asystem as recited in claim 16, wherein said programmable printcontroller adjusts said color intensity of said third pixel to anaverage intensity of said second pixel and said third pixel.
 20. Asystem as recited in claim 16, wherein said first pixel and said secondpixel are near an edge of the image.
 21. A system as recited in claim16, wherein each of said pixels further comprises a plurality of colors.